Global oceanic and atmospheric stability of oxygen
Prehistoric atmospheric oxygen production began through water vapour dissociation, caused by powerful UV radiation from space, followed by a secondary reaction involving the formation of ozone (O3) from O2. The level of oxygen, called Urey level, was kept stable by the feedback process where UV radiation is reduced through absorption by the ozone produced. The equilibrium level thus obtained is estimated at 1 % of the actual level, i.e. about 0.02 vol%. At 3.2 billion years ago an initial form of primitive photosynthesis started, keeping the oxygen level at about 0.2 vol% (Pasteur level), followed at 1.8 billion years ago by photosynthesis using chlorophyll pigments (Duursma and Boisson 1994). Photosynthesis started using chlorophyll pigments. This occurred first in water systems below a column of about 10 m water, out of reach of the still high level of hazardous UV radiation, which was absorbed by this water layer. Later, when a sufficient level of atmospheric O2 was built up, and consequently of an increased ozone level, this ozone absorbed the major part of hazardous UV radiation. As a result, photosynthesis manifested itself in surface waters and on land.
KeywordsAtmospheric Oxygen Humus Formation Atmospheric Stability Chlorophyll Pigment Burial Rate
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